Středoevropský technologický institut

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    Damage Evolution in Thermomechanical Loading of Stainless Steel
    (Elsevier, 2016-06-20) Petráš, Roman; Škorík, Viktor; Polák, Jaroslav
    Superaustenitic stainless steel Sanicro 25 has been subjected to in-phase and out-of-phase thermomechanical fatigue (TMF). Different amplitudes of mechanical strain and the changes of the temperature in the interval 250 to 700°C were applied to standard cylindrical specimens. Early fatigue damage has been studied using scanning electron microscopy combined with FIB cutting and EBSD imaging. TMF loading resulted first in developing thin oxide layer. In in-phase loading grain boundaries were preferentially oxidized and fatigue cracks developed by alternating oxidation and cracking. Fatigue cracks developed rapidly in oxidized grain boundaries and propagated intergranularly. During out-of-phase TMF loading the cracked oxide layer resulted in local oxidation and crack initiation. The crack grew transgranularly.
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    Fracture Resistance of 14Cr ODS Steel Exposed to a High Temperature Gas
    (MDPI, 2017-12-01) Hojná, Anna; Michalička, Jan; Hadraba, Hynek; Di Gabriele, Fosca; Duchoň, Jan; Rozumová, Lucia; Husák, Roman
    This paper studies the impact fracture behavior of the 14%Cr Oxide Dispersion Strengthened (ODS) steel (ODM401) after high temperature exposures in helium and air in comparison to the as-received state. A steel bar was produced by mechanical alloying and hot-extrusion at 1150 °C. Further, it was cut into small specimens, which were consequently exposed to air or 99.9% helium in a furnace at 720 °C for 500 h. Impact energy transition curves are shifted towards higher temperatures after the gas exposures. The transition temperatures of the exposed states significantly increase in comparison to the as-received steel by about 40 °C in He and 60 °C in the air. Differences are discussed in terms of microstructure, surface and subsurface Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) observations. The embrittlement was explained as temperature and environmental effects resulting in a decrease of dislocation level, slight change of the particle composition and interface/grain boundary segregations, which consequently affected the nucleation of voids leading to the ductile fracture.